Phosphine‐Catalyzed Chemoselective [4+3] Cycloaddition of Alminine Esters and β′‐acetoxy Allenoates for Divergent Synthesis of Azepines

Text. A general method for the synthesis of structural diversity and complexity of azepines from aldimine esters and β′‐acetoxy allenoates is reported. Under phosphine catalysis, a [4+3] cycloaddition for the formation of 1,3‐dihydro‐2H‐azepine‐2,2,4‐tricarboxylates was achieved with broad substrate scope under mild reactions. A switchable process was given and a variety of important 2,3‐dihydrochromeno[4,3‐b]azepin‐6(1H)‐ones were selectively formed when the reaction was performed in the presence of Cs2CO3 and PPh3, which involved an intramolecular ester group migration and subsequent lactonization of 1,3‐dihydro‐2H‐azepine‐2,2,4‐tricarboxylates. Besides easy handle process, high synthetic value of resulting products, it is worth to note that this work showed the novel example of 1,5‐ethoxycarbonyl migration.